JP2005256630A - Spark ignition type direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark ignition type direct injection engine capable of performing uniform combustion of excellent characteristic by improving homogeneity of an air-fuel mixture. <P>SOLUTION: This spark ignition type direct injection engine is provided with a combustion chamber 10, an ignition plug 32, an intake valve 20, an exhaust valve 22 opposed to the intake valve, an injector 36 adjoining the intake valve, and a fuel injection control means. The injector is provided with a plurality of nozzle holes, and at least one of the nozzle holes is arranged so that its axis points to the exhaust valve, while at least one of the nozzle holes is arranged so that its axis points to a crown face of a piston. The fuel injection control means performs divided injection control for injecting fuel from the injector divided in an intake stroke and a compression stroke in a high load or high rotation region. Injection in the compression stroke is performed in at least two steps from the middle stage of the compression stroke onward. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spark ignition direct injection engine, and particularly to a spark ignition direct injection engine including an injector having a plurality of injection holes.

  There is known a spark ignition type direct injection engine provided with an injector for directly injecting fuel into a combustion chamber. This type of engine is configured to improve fuel efficiency by performing fuel injection during the compression stroke, causing the air-fuel mixture to be unevenly distributed near the spark plug and performing stratified combustion. The present invention has been developed based on such a technique.

  In the direct injection engine as described above, under a predetermined condition such as at the time of full load, fuel is injected during the intake stroke, and the air-fuel mixture is uniformly distributed in the cylinder and burned uniformly. However, in a direct injection engine, since the mixture is unevenly distributed in the vicinity of the spark plug and is suitable for stratified combustion, when the uniform combustion is performed by fuel injection in the intake stroke, the mixture is The required torque cannot be obtained due to poor vaporization or unevenness, and problems such as smoke, particulates, and HC may occur at full load.

  The inventors of the present invention promote the vaporization / mixing of the injected fuel in the direct injection engine by devising the direction of the axis of the injector nozzle (center axis of fuel injection) and the injection timing from the injector. It was found that the homogeneity of the air-fuel mixture in the combustion chamber can be improved even in a region where the engine load is high.

  The present invention has been made based on such knowledge, and an object thereof is to provide a spark ignition type direct injection engine capable of improving the homogeneity of the air-fuel mixture and performing uniform combustion with excellent characteristics. To do.

  According to the present invention, a combustion chamber composed of a cylinder, a cylinder head, and a piston, an ignition plug disposed in the upper center of the combustion chamber, an intake valve disposed on a ceiling portion of the combustion chamber, and the ignition An exhaust valve disposed at a position facing the intake valve across the plug, an injector disposed adjacent to the intake valve and injecting fuel into the combustion chamber, and fuel injection for controlling fuel injection from the injector A spark ignition direct injection engine including a control means, wherein the injector includes a plurality of injection holes, and at least one of the injection holes is disposed such that an axis thereof is directed to the exhaust valve; At least one of the nozzle holes is arranged such that its axial center is directed to the crown surface of the piston, and the fuel injection control means performs an intake stroke and a compression stroke in a high load or high rotation range. Thus, there is provided a spark ignition direct injection engine characterized in that split injection control for injecting fuel from the injector is performed, and the injection in the compression stroke is performed at least twice after the middle of the compression stroke. .

According to such a configuration, in a high load or high speed region, compression is performed in a state where the air-fuel mixture is unevenly distributed in the upper portion of the combustion chamber by intake stroke injection and the in-cylinder pressure is increased and the movement of the injected fuel is suppressed. In the first injection after the middle of the stroke, the air-fuel mixture is unevenly distributed in the space around the spark plug from the exhaust side, and the second after the middle of the compression stroke performed in a state where the piston approaches the top dead center and the injected fuel is pushed up. The air-fuel mixture is unevenly distributed in the space below the spark plug by the injection of the eyes. As a result, the air-fuel mixture is uniformly dispersed throughout the combustion chamber by the injection in the intake stroke and the two injections in the compression stroke. For this reason, the homogeneity of the air-fuel mixture in a high load or high rotation region is improved, and smoke and HC are reduced.
Further, since fuel injection is performed during the compression stroke in which the in-cylinder temperature rises, the in-cylinder temperature is lowered by the latent heat of vaporization of the injected fuel, and knocking is suppressed.

  According to another preferred aspect of the present invention, the fuel injection control means causes the injection in the intake stroke to be executed in the middle of the intake stroke.

According to another preferred aspect of the present invention, the fuel injection control means includes a fuel injection amount Q1 of the injection in the intake stroke, a fuel injection amount Q2 of the first injection in the compression stroke, and a second in the compression stroke. The fuel injection amount is controlled so that the fuel injection amount Q3 of the subsequent injections satisfies the relationship of Q1> Q2 ≧ Q3.
According to such a configuration, necessary torque is ensured while reducing smoke and HC emission.

  According to another preferred aspect of the present invention, the fuel injection control means has a fuel injection amount so as to satisfy a relationship of Q2> Q3 in a high load region and to satisfy a relationship of Q2 ≧ Q3 in other regions. To control.

  According to another preferred aspect of the present invention, there are provided a plurality of the nozzle holes arranged such that the axis is directed to the crown surface of the piston, and the axes of the nozzle holes are positioned at intermediate positions of the cylinder. Oriented to the crown of the piston.

According to another preferred aspect of the present invention, a recess is formed in the crown surface of the piston, and the axial centers of the plurality of nozzle holes are directed to the opening edge of the recess.
According to such a configuration, since the fuel is injected to the opening edge of the concave portion of the piston crown surface, the fuel colliding with the edge portion is effectively diffused and mixing is promoted.

  ADVANTAGE OF THE INVENTION According to this invention, the spark-ignition type direct injection engine which can improve the homogeneity of air-fuel | gaseous mixture and can perform the uniform combustion of the outstanding characteristic is provided.

Hereinafter, a configuration of a spark ignition direct injection engine according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a spark ignition direct injection engine 1 according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the vicinity of the combustion chamber of the engine.
The engine 1 includes a cylinder block 4 in which four cylinders 2 (only one is shown in FIG. 1) arranged in series are formed, and a cylinder head 6 arranged on the cylinder block 4. . A piston 8 is disposed in the cylinder 2 so as to be able to reciprocate in the vertical direction.

  3 is a plan view showing a crown surface of the piston 8, and FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. As shown in FIGS. 3 and 4, a concave cavity 9 that opens upward is formed on the crown surface of the piston 8. As shown in FIG. 3, the cavity 9 has a semi-rugby ball shape having an oval opening at the upper end. Further, as shown in FIG. 4, the cavity 9 has an opening edge 9a having an arcuate cross section (R shape).

A combustion chamber 10 is formed between the piston 8 and the cylinder head 6. As shown in FIG. 2, the combustion chamber 10 is a so-called pent roof type combustion chamber having two inclined surfaces extending from a substantially central portion of the ceiling portion of the cylinder 2 to the vicinity of the lower end surface of the cylinder head 6.
On the other hand, a crankshaft 12 is rotatably supported below the piston 8 in the cylinder block 4, and the crankshaft 12 and the piston 8 are connected via a connecting rod 14.

  As shown in FIG. 1 and FIG. 2, the cylinder head 6 has two intake ports 16 and two exhaust ports 18 in parallel (only one of them is shown in FIGS. 1 and 2). It is formed with. Each of the two intake ports 16 is opened on one inclined surface of the combustion chamber, and an intake valve 20 that is opened and closed at a predetermined timing is seated on each intake port 16. Each intake valve 20 has a generally circular shape and includes a valve umbrella portion 20a that opens and closes the intake port 16, and a rod-shaped stem 20b that extends from the center of the valve umbrella portion 20a. The two exhaust ports 18 are seated with exhaust valves 22 that are opened on the other inclined surface of the combustion chamber and are opened and closed at a predetermined timing.

  As shown in FIG. 1, an intake passage 24 that communicates with the intake port 16 of each cylinder 2 is connected to one side of the engine 1. The intake passage 24 is for supplying the intake air filtered by an air cleaner (not shown) to the combustion chamber 10 of the engine 1. The intake passage 24 is sucked into the engine 1 in order from the upstream side to the downstream side. A hot wire air flow sensor 26 for detecting the amount of air, an electric throttle valve 28 for restricting the intake passage 24, and a surge tank 30 are arranged. The electric throttle valve 28 is not mechanically connected to an accelerator pedal (not shown) and is driven by an electric drive motor (not shown).

  Further, the intake passage 24 is branched into independent passages connected to the cylinders 2 on the downstream side of the surge tank 30, and the downstream end portion of the independent passages is further branched into two to provide two intake air for each cylinder. Each port 16 is connected.

  A spark plug 32 is disposed at the center of the upper portion of the combustion chamber 10 at substantially the center of the four intake / exhaust valves 20, 20, 22, 22. An electrode 32 a at the tip of the spark plug 32 is located at a position protruding a predetermined distance from the ceiling of the combustion chamber 10, and an ignition circuit 34 is connected to the base end of the spark plug 32. The ignition plug 32 is energized at a predetermined timing.

An injector 36 is attached between the intake valves 20 at the peripheral edge of each combustion chamber 10. The injector 36 is a so-called multi-hole injector in which a plurality of injection holes are formed at the tip, and is disposed so as to face the exhaust valve 22 with the electrode portion 32a of the spark plug 32 interposed therebetween.
Each injector 36 is connected to a fuel distribution pipe 38. The fuel distribution pipe 38 supplies high-pressure fuel supplied from the fuel supply system 40 to each injector 36.

  As shown in FIG. 1, an exhaust passage 42 that exhausts exhaust gas from the combustion chamber 10 is connected to the other side of the engine 1. The upstream end of the exhaust passage 42 is an exhaust manifold 44 that is branched and connected to the exhaust port 18 of each cylinder 2. A linear O2 sensor 46 for detecting the oxygen concentration in the exhaust gas is disposed at the collection portion of the exhaust manifold 44. The linear O2 sensor 46 detects the air-fuel ratio based on the oxygen concentration in the exhaust.

  Further, the upstream end of the exhaust pipe 48 is connected to the collecting portion of the exhaust manifold 44. A three-way catalyst 50 and a NOx absorption catalyst 52 are attached to the exhaust pipe 48 in order from the upstream side to the downstream side. The NOx absorption catalyst 52 adsorbs NOx when the oxygen concentration in the exhaust gas is high, releases NOx adsorbed as the oxygen concentration decreases, and reduces the released NOx by HC, CO, etc. in the exhaust gas. It is an adsorption reduction type catalyst.

  The exhaust pipe 48 is connected to an upstream end of an EGR passage 54 that recirculates a part of the exhaust gas to the intake system. The downstream end of the EGR passage 54 is connected to the intake passage 24 between the throttle valve 28 and the surge tank 30. The EGR passage 54 is provided with an EGR valve 56 whose opening degree can be adjusted electrically.

  As shown in FIG. 1, the engine 1 includes an ECU (engine control unit) 58. The ECU 58 receives output signals from various sensors such as a crank angle sensor 60 that detects the rotation angle (engine speed) of the crankshaft 12, the airflow sensor 26, the linear O2 sensor 46, and the accelerator opening sensor 62, Based on the input output signal, the operations of the ignition circuit 34, the injector 36, the electric throttle valve 28, the EGR valve 56, and the like are controlled.

Fig.5 (a) shows the control map used by the fuel-injection control performed in the engine 1 of this embodiment. As shown in FIG. 5 (a), in the engine of the present embodiment, split injection control in which fuel is injected separately into an intake stroke and a compression stroke, and fuel is injected once in an intake stroke, under the control of the ECU 58. The batch injection control to be performed is performed by switching.
That is, in the engine of the present embodiment, split injection is performed from a low load in the engine low rotation region, a high load in the middle rotation region, a medium load in the high rotation region, and a batch injection in the other regions. Yes. In general, in a direct-injection gasoline engine, the air-fuel mixture is easily homogenized in the middle rotation region. Therefore, in the present embodiment, the split injection is performed only in the high load region in the middle rotation region. In the middle rotation region, a configuration in which divided injection is not performed even in a high load region may be employed.

  Also, as shown in Fig. 5 (b), the control characteristics are set so that the load for starting batch injection or split injection becomes high in the high rotation range for an engine aimed at homogenization in the high rotation range. May be. In the case of such an engine, the homogeneity deteriorates in the collective injection as the rotational speed becomes lower. Therefore, the load for starting the divided injection is set lower as the rotational speed becomes lower.

  Further, in an engine aiming at homogenization in a low rotation range, as shown in FIG. 5C, control characteristics for performing split injection on the high load side in the entire rotation range may be set.

  In the divided injection of the present embodiment, as shown in the time chart of FIG. 6, fuel injection is performed three times in total, once in the intake stroke and twice in the compression stroke. The injection in the intake stroke is preferably performed in the middle of the intake stroke where the flow velocity of the intake flow is high. Specifically, the injection timing in the intake stroke is such that the injection starts at 0 ° to 100 ° after top dead center (ATDC) and completes at 100 ° to 200 ° after top dead center (ATDC). It is preferable to set the injection timing in the stroke, and it is more preferable to set so that the injection timing exists in the range of 60 ° to 120 ° after top dead center (ATDC).

  The first injection in the compression stroke is, for example, before the compression top dead center (BTDC) 30 ° to 140 after the middle of the compression stroke, which is the time when the cylinder pressure becomes high and the movement of the injected fuel is suppressed. It is preferably performed at the time of °.

  Further, the second injection in the compression stroke is, for example, before the compression top dead center (BTDC) 0 ° to 90 ° after the middle of the compression stroke, which is a time when the piston approaches the top dead center and the injected fuel is pushed up. It is preferred to be done at the time.

The injection amount Q1 of the fuel injection in the intake stroke, the injection amount Q2 of the first fuel injection in the compression stroke, and the injection amount Q3 of the second fuel injection in the compression stroke are: Q1> Q2 ≧ Q3 It is set to satisfy the relationship.
Further, the fuel injection amount is set so that the relationship of Q2> Q3 is satisfied in the high load region, and the relationship of Q2 ≧ Q3 is satisfied in the other regions.

  Further, in the region where the divided injection is not performed, uniform fuel is executed in which fuel is injected all at once in the intake stroke.

  Next, the arrangement of the plurality of nozzle holes formed in the injector 36 will be described. FIG. 7 is a drawing showing the arrangement of a plurality of nozzle holes at the tip of the injector 36 or the position where injection is aimed. As shown in FIG. 7, the injection hole 64 of the injector 36 according to the present embodiment includes two injection holes (upper injection holes) 64 a and 64 b arranged above, and four injection holes (lower injection holes) arranged below. 64c, 64d, 64e, 64f. In this embodiment, each nozzle hole has the same diameter (about 0.15 mm), and the spread (injection angle) of the fuel injected from each nozzle hole is also the same.

  The axial centers 66a and 66b of the upper injection holes 64a and 64b, that is, the fuel injection direction (center axis of the injected fuel) are directed to the exhaust valve 22 through the left and right regions of the electrode portion 32a of the spark plug 32, respectively. Are arranged to be.

  The lower nozzle holes 64c, 64d, 64e, and 64f have their axial centers 66c, 66d, 66e, and 66f, when the piston 8 is located at an intermediate position in the height direction of the cylinder 2 (cylinder). It is arranged to point to. Specifically, the lower nozzle holes 64c, 64d, 64e, and 64f have regions in the vicinity of the upper edge 9a of the cavity 9 of the crown surface of the piston 8 in which the axial centers 66c, 66d, 66e, and 66f are located at intermediate positions (indicated by dotted lines in FIG. 3). Are arranged so as to be oriented. Therefore, the fuel injected from the lower nozzle holes 64c, 64d, 64e, 64f when the piston 8 is at the intermediate position collides with the region indicated by the dotted line in FIG.

  Further, as shown in FIG. 8, each of the nozzle holes 64a, 64b, 64c, 64d, 64e, and 64f has an opening angle Θ with respect to the axial centers 66x and 66y of the two adjacent nozzle holes 64x and 64y. Are arranged so as to have an angle larger than the sum of ½ of the injection angles α and β from the respective nozzle holes. Such an arrangement prevents the fuel injected from each nozzle from coming into contact with each other.

  According to the engine of the present embodiment having such a configuration, when split injection is performed, the amount of fuel injected in the compression stroke is set to be smaller than the amount of fuel injected in the intake stroke. Therefore, the occurrence of smoke or the like is suppressed without the fuel injected in the compression stroke being vaporized. In particular, when the load is likely to cause smoke, the second injection amount in the compression stroke is set to be smaller than the first injection amount, so that the occurrence of smoke is effectively suppressed.

  Further, since the axis of the lower nozzle hole directed to the crown surface of the piston 8 is directed to the opening edge 9a of the arc 9 (R-shaped) cavity 9, when the piston 8 is at the intermediate position, The fuel injected from the nozzle holes 64c, 64d, 64e, and 64f collides with the arcuate edge 9a and quickly diffuses to the surroundings. For this reason, the homogeneity of the air-fuel mixture is improved.

The present invention is not limited to the above-described embodiments, and various changes or modifications can be made within the scope of the technical matters described in the claims.
The number and arrangement of the nozzle holes of the injector are not limited to those of the above embodiment. Moreover, in the said embodiment, although it was the structure which performs fuel injection twice in a compression stroke in a high load or low rotation, or a high rotation area | region, the structure which injects three times or more in a compression stroke may be sufficient.

It is drawing which shows schematic structure of the spark ignition direct injection engine of preferable embodiment of this invention. It is sectional drawing to which the combustion chamber vicinity of the engine of FIG. 1 was expanded. It is a top view which shows the piston crown surface of the engine of FIG. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. 2 is a control map of fuel injection control performed in the engine of FIG. 1. It is a time chart of the fuel injection at the time of the division | segmentation injection in the engine of FIG. It is drawing which shows arrangement | positioning of the nozzle hole in the engine of FIG. It is a schematic drawing which shows the relationship between the angle between the axial centers of an adjacent nozzle hole, and the injection angle from each nozzle hole.

Explanation of symbols

1: Engine 2: Cylinder 10: Combustion chamber 20: Intake valve 22: Exhaust valve 32: Spark plug 36: Injector 64: Injection port 64a, 64b: Upper injection port 64c, 64d, 64e, 64f: Lower injection port 66a, 66b, 66c, 66d, 66e, 66f: axial center of the nozzle

Claims (6)

A combustion chamber composed of a cylinder, a cylinder head, and a piston; an ignition plug disposed at an upper center of the combustion chamber; an intake valve disposed on a ceiling portion of the combustion chamber; and the intake air sandwiching the ignition plug An exhaust valve disposed at a position opposite to the valve; an injector disposed adjacent to the intake valve for injecting fuel into the combustion chamber; and fuel injection control means for controlling fuel injection from the injector. A spark ignition direct injection engine,
The injector includes a plurality of nozzle holes;
At least one of the nozzle holes is arranged such that its axis is directed to the exhaust valve;
At least one of the nozzle holes is disposed such that an axis thereof is directed to a crown surface of the piston;
The fuel injection control means performs divided injection control in which fuel is injected from the injector in an intake stroke and a compression stroke in a high load or high rotation range, and the injection in the compression stroke is performed at least after the middle of the compression stroke. Done in two parts,
This is a spark ignition direct injection engine. The fuel injection control means performs injection in the intake stroke in the middle of the intake stroke;
The spark ignition direct injection engine according to claim 1. The fuel injection control means includes: a fuel injection amount Q1 of the injection in the intake stroke; a fuel injection amount Q2 of the first injection in the compression stroke; and a fuel injection amount Q3 of the second and subsequent injections in the compression stroke. , Control the fuel injection amount so as to satisfy the relationship of Q1> Q2 ≧ Q3.
The spark ignition direct injection engine according to claim 1 or 2. The fuel injection control means controls the fuel injection amount so as to satisfy a relationship of Q2> Q3 in a high load region and satisfy a relationship of Q2 ≧ Q3 in other regions;
The spark ignition direct injection engine according to claim 3. A plurality of the nozzle holes arranged such that the axis is directed to the crown surface of the piston are provided, and the axis of the nozzle holes is directed to the crown surface of the piston located at an intermediate position of the cylinder.
The spark ignition direct injection engine according to any one of claims 1 to 4. A recess is formed in the crown of the piston,
The axial centers of the plurality of nozzle holes are directed to the opening edge of the recess,
The spark ignition direct injection engine according to claim 5.

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